1. Field of the Invention
The present invention relates to a solid multi-piece golf ball which provides excellent flight performance, controllability on approach shots, xe2x80x9cfeelxe2x80x9d upon impact, and durability.
2. Prior Art
Solid multi-piece golf balls having a solid core and a cover composed of at least two layers have already been proposed as golf balls which meet the requirements of professionals and other skilled golfers. For example, JP-A 7-24085 discloses a golf ball with a hard inner cover/soft outer cover construction in which the inner cover layer has a greater hardness than the outer cover. JP-A 10-151226 discloses a solid multi-piece golf ball of the same type which has an improved spin performance, durability and flight distance.
However, such improvements remain inadequate. A need continues to be felt for golf balls having certain qualities desired in particular by professionals and other skilled golfers, such as better spin performance when hit with an iron or on approach shots, and improved xe2x80x9cfeelxe2x80x9d upon impact, durability and rebound energy.
It is therefore an object of the invention to provide a solid multi-piece golf ball having excellent flight performance, improved spin performance when hit with an iron and on approach shots, and improved feel upon impact, durability and rebound.
We have found that the synergistic effects achieved by optimizing certain essential conditions in a golf ball serve to increase the distance traveled by the ball, provide the ball with excellent spin performance when hit with an iron and on approach shots, and endow the ball with good cracking resistance, good durability to topping, good scuff resistance and a good feel upon impact, resulting in the exceptional performance desired in particular by professionals and other skilled golfers.
Accordingly, the invention provides a solid multi-piece golf ball having a solid elastic core, a cover composed of at least one layer enclosing the core, and an intermediate layer composed of a thermoplastic material between the core and the cover. The core, when subjected to a load of 1274 N (130 kgf) from an initial load of 98 N (10 kgf), undergoes a deformation of 3.2 to 6.5 mm. The cover has a Shore D hardness of 45 to 55 and the intermediate layer has a Shore D hardness in a range of 54 to 65 and higher than the Shore D hardness of the cover. The cover and the intermediate layer have a combined thickness, defined as (cover thickness+intermediate layer thickness), of 2.3 to 3.5 mm. The cover and the intermediate layer have a thickness ratio, defined as (cover thickness)/(intermediate layer thickness), of 0.48 to 0.84.
Preferably, the cover is composed primarily of a material selected from the group consisting of thermoplastic and thermoset polyurethane elastomers, polyester elastomers, ionomer resins, polyolefin elastomers and mixtures thereof.
The intermediate layer is typically made of a resin composition containing at least 30 parts by weight of ionomer resin, which resin composition preferably includes:
(a) 100 parts by weight of an olefin/unsaturated carboxylic acid random copolymer, an olefin/unsaturated carboxylic acid/unsaturated carboxylic acid ester random copolymer, a metal ion neutralization product of either type of copolymer, or a mixture of any of the copolymers and the neutralization products thereof;
(b) 5 to 80 parts by weight of a fatty acid having a molecular weight of at least 280 or a derivative thereof; and
(c) 0.1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing the acid groups within components (a) and (b).
In one preferred embodiment, the golf ball of the invention has an adhesive layer between the cover and the intermediate layer.